As a switching power-supply device which performs output voltage control by a switching operation, a step-down chopper type switching power-supply device is known.
The step-down chopper type switching power-supply device includes: a series circuit of a switching element which is connected to a DC power source and a diode; a series circuit which includes an inductor and a capacitor and is connected to both ends of the diode; a control IC (integrated circuit), which detects the regenerative voltage of the inductor in an OFF period of the switching element and controls the switching element based on an error voltage between the detected regenerative voltage and a reference voltage such that the regenerative voltage of the inductor becomes the reference voltage; and an auxiliary power supply circuit which supplies power-supply voltage to the control IC by using the regenerative voltage of the inductor in the OFF period of the switching element.